In the field of mining machines such as continuous miners and the like, road working machines such as road planers and the like, and earth moving machines such as mechanized shovels and the like, it is common practice to provide the machine with a driven element having a plurality of bits mounted thereon. The term "bit" should be considered broadly enough to cover mining machine cutter bits and road working and earth moving machine digger teeth. It is common practice on these machine to provide each bit with a bit holder and to provide each bit holder with a base member by which it is attached to the driven element of the machine. In some instances, the base member may constitute an integral, one-piece part of the driven element of the machine.
As will be readily understood by one skilled in the art, bits are subject to great wear and have a relatively short working life. As a consequence, the bit must be easily replaceable with respect to the bit holder. Similarly, the bit holder is also subject to wear, but generally not as severe wear as is encountered by the cutter bit. Nevertheless, it is important that the bit holder be readily replaceable with respect to its base member. It is to the replaceable mounting of a bit holder in its base member that this invention is directed. While not intended to be so limited, for purposes of an exemplary showing, the present invention will be described in its application to bit ;holder and base member assemblies of mining machines. It will be apparent to one skilled in the art that the teachings of the present invention are directly applicable to bit holder and base member assemblies of road working and earth moving machines, as well.
There are many types of mining machines, all-of which are characterized by the presence of one or more primary drive members to which there is affixed at least one, and generally a plurality of base members, adapted to receive bit holders and cutter bits.
The driven member, driven by appropriate prime mover means, may take a number of forms such as a chain, a rotating wheel, a rotating arm, or a rotating drum. Mining machines, themselves, are of various types including undercutting machines, continuous mining machines, and long wall mining machines.
Recognizing the necessity for bit holder and base member assemblies wherein the bit holder is readily removable from the base member, prior art workers devised many arrangements. For example, a number of "pin-on" arrangements have been developed, and the arrangement taught in U.S. Patents Re 28,310 and 4,163,581 are exemplary. Similarly, a number of "wedge-on" arrangements have been devised, of which the teachings of U.S. Pat. Nos. 4,057,294 and 4,275,929 are exemplary. One of the best known and most heavily used systems for removably mounting a bit holder in a base member is set forth in U.S. Pat. No. 4,337,980. The teachings of this patent are incorporated herein by reference.
Briefly, U.S. Pat. No. 4,337,980 sets forth a novel wedge arrangement for affixing a tool mounting means onto a base member in such manner that substantially no relative movement occurs between the mounting means and the base member, thus vastly improving the working lives of both. According to the wedge arrangement of this patent, the bit holder is provided with a tapered portion and the base member is provided with a tapered cavity to receive the tapered portion of the bit holder. That part of the base member which defines the cavity completely surrounds that part of the tapered portion of the bit holder seated therein for at least a portion of the length of the tapers, so that the wedge arrangement is 360.degree. in scope. The resultant cutting forces encountered during operation of the mining machine serve to urge the tapered portion of the bit holder into its seated position within the tapered cavity of its base member. Contact between the tapered portion of the bit holder and the base member cavity is such that there is no rotation, wobble or other relative movement between the two when the tapered portion of bit holder is properly seated in the tapered cavity of the base member. This contact may also be 360.degree. in scope, although this is not the case in all embodiments of this reference:.
In all the embodiments illustrated and described in U.S. Pat. No. 4,337,980, retaining means are taught which retain the tapered portion of the bit holder in its seated position within the tapered cavity of the base member, and urge the bit holder tapered portion into full seated position within the base member while simultaneously precluding rotation of the bit holder tapered portion within the base member tapered cavity. The reference teaches a number of different types of retaining means to retain the bit holder in the base member and to urge the bit holder to its fully seated position. These retaining means include bolts, wedging-type C-shaped retainers, wedges and deformable resilient means. Perhaps the most common means for retaining the bit holder within the base member, taught in U.S. Pat. No. 4,337,980, is the provision of a cylindrical portion at the end of the tapered portion of the bit holder. The tapered cavity of the base member extends through the base member and the cylindrical portion of the bit holder also extends through the base member. The cylindrical portion is threaded and is adapted to receive a nut which tightens against a rearward surface of the base member.
The present invention is intended to constitute an improvement upon the teachings of U.S. Pat. No. 4,337,980. In the field, it has been found that manipulation of the retaining means for the bit holder with respect to the base member is sometimes difficult and time consuming. In U.S. Pat. No. 4,337,980 it is hinted that, under some circumstances, the wedging action alone may be sufficient to prevent rotation of the tapered portion of the bit holder within the tapered cavity of the base member and removal of the tapered portion of the bit holder from the tapered cavity of the base member. The reference does not teach or suggest, however, under what circumstances this might be so and just how this might be accomplished. All of the embodiments illustrated, described and claimed in U.S. Pat. No. 4,337,980 are provided with retaining means to urge the bit holder to its fully seated position within the base member and to maintain it there.
The present invention is based upon the discovery that if the tapers of the bit holder portion and the corresponding tapered cavity of the base member have a common angularity up to about 12.degree., and preferably in the range of from about 6.degree. to about 12.degree., a retaining means for urging and maintaining the tapered portion of the bit holder in the tapered cavity of the base member is not required. The bit holder will remain fully seated and non-rotatable within the base member cavity during operation of the mining machine under substantially all conditions of cutting and over a wide range of materials being cut. The bit holder is preferably provided with a safety ring, as will be described hereinafter. It has further been found that the preferred angularity of the taper of the tapered portion of the bit holder and the tapered cavity of the base member will vary within the above-stated range, depending upon the type of mining machine employed. When replacement of the bit holder is required, it can be removed from the base member by an appropriate prying action.
It is taught in U.S. Pat. Nos. 4,337,980 that there are a number of types of mining machine cutter bits including those which rotate within the shank receiving perforation of the bit holder, and those which do not. Prior art workers have used many means to secure cutter bit shanks in the shank receiving perforations of bit holders. The retaining means include set screws and other mechanical latching or locking devices and resilient retaining means enabling a "knock-in", "pry-out" engagement between the cutter bit and the bit holder. These include retainers developed specifically for non-rotating bits and others developed specifically for rotating bits. The nature of the cutter bit and whether or not it is a rotatable cutter bit do not constitute limitations of the present invention. In most instances, the cutter bit will comprise an elongated shank, at least a portion of which is rotatively or non-rotatively receivable within the shank receiving perforation of the bit holder. The cutter bit shank will terminate, at at least one end thereof, in a cutting head bearing a cutting tip, or simply in a cutting tip. In some instances, the cutter bits are double ended, so that when one cutting end becomes badly worn, it can be replaced by the other cutting end.